Process of making mineral wool batts



Patented May 30, 1944 PROCESS OF MAKING MINERAL WOOL BATTS Virgil E. Meharg, Bloomfield. N. 1., assignor to Bakelite Corporation, New York, N. Y., a corpo ration of New Jersey Application February 17, 1940. Serial No. 319,465

No Drawing.

4 Claims.

This invention relates to the production of highly porous materials as batts of glass wool fibers bound at intersection points with a synthetic resin.

For many purposes in the arts, for instance for heat insulation purposes, it is desirable to have a low cost highly porous non-inflammable material. It is relatively simple to prepare a somewhat porous material where the fibers are used merely as fillers in a molded mass of porous binder, but such a material is too expensive tor a low cost insulation as too much resin is used. However, it is highly desirable to use the phenolaldehyde resins as binders since, when reacted, they are non-inflammable but, so tar as I am aware, no method has heretofore been devised which will place the binder, in batts, where it will serve as a binder and yet not waste the resin by coating fibers where it is generally unnecessary that they be coated.

For the purpose of explaining the invention it should be understood that the batts are made of mineral wool or glass wool or slag wool fibers, designated generically hereafter as glass wool" fibers,. that is fibers manufactured from melted rock, sand, clay, slag, glass or similar material by any of the commonly used processes, for instance blowing, drawing, etc. These manufactured glass wool fibers differ from other fibers, in that they are non-porous and non-cellular and have a relatively smooth surface, whereas natural fibers are porous and absorptive and the naturally occurring fibers, for instance cotton and asbestos have relatively rough surfaces in the form in which they are used. Substantially the only natural fiber which is inherently non-inflammable is asbestos, the ffibers of which (as the term is commonly used) are composed of bundles of extremely fine filaments. The filaments are too weak for use in batts and cannot be separated from one another by any commercially practical process and in the asbestos fibers they protrude from the main surface of the fiber making the surface rough.

In addition to the above characteristics, there are other characteristics of glassv wool fibers which should be taken into consideration, namely the flexibility and resiliency of the fibers. The mineral bodies, for instance, slag, glass, etc. from which the glass wool is made, are usually thought of as being hard and brittle. This is generally true for bodies of relatively large size, such as tumblers, bottles, windowpanes,

etc. but fibers are so small that they can be quite flexible and have a surprising resiliency. The character of the fiber has a bearing on the invention as will later be explained.

When the batts are made the fibers are built up on one another in an indiscriminate arrangement in any suitable manner, for instance by blowing the fibers onto a foraminous belt or by blowing the fibers into a container and permitting them to fall to the bottom. Thus the fibers are not laid parallel nor at right angles nor in any regular pattern. If the batt thus formed is too porous it may be compressed somewhat but the final result is a fibrous mass in which the fibers extend in every direction and contact one another at irregular intervals. It will thus be understood that for any individual fiber the area or length of contact between it and other fibbers is much less than the surface area or length of the fiber which is not in contact with other fibers.

For the usual batts, it is desired to overcome some of the felting tendency of the fibers so that the batts may be held somewhat to a predetermined size and yet not have the fibers broken as this would decrease the strength of the batt and the small pieces of the broken fiber would gradually sift out of the batt so that they would be useless in preventing the circulation of air and thus would decrease the heat insulation value of the batt. It is thus desirable not to kill the. resiliency of the batt, or decrease its heat insulating value but at the same time strengthen the batt and so prepare it that it can be held substantially to a predetermined dimension. It is also desirable to make the batt at as low a cost as is possible.

I have conceived that if a glass wool batt could be so treated with a. binder that substan tially all of the binder is located at the points at which the fibers intersect one another and substantially none of the binder is on the fibers between the points of intersection, that is if a bead or hinder could be placed only at the fibercontact or intersection points, the batt would have the resiliency resulting from what, in effect is short length fibers, the batt could be held to a predetermined size, the fibers would not break and sift out of the batt, the batt would be materially strengthened and a minimum of binder could be used. Obviously, for binding purposes, it is useless to coat with a binder the length or surface area of the fiber which is not in contact with other fibers as this represents a waste of binder but it is important to concentrate the binder on the fibers at the areas where they intersect. n is also desirable to distribute the binder in such a manner that where there happen to be relatively more intersections between a given fiber and other fibers, there is relatively less binder at each intersection, and where there happen to be relatively fewer intersections there is more binder at each contact as, for support, a fiber should be more firmly bound to an intersecting fiber where there is a reater distance between intersections than where there are more intersections and a smaller distance between them.

If it were commercially feasible .in the usual batts, that is if costs did not have to be considered, it would, of course, be possible to use so much binder that every intersection wouldhave much more than enough binder to provide sufllcient strength at the intersections, in fact each fiber could be coated throughout its entire length, but, as previously stated, this represents a waste of binder in the usual batt and also the batt would conduct heat more readily at the added mass of resin would provide more paths by which heat could be conducted. Furthermore, the batt would not have the resiliency usually desired.

In some instances, as will later be explained, it may be desirable in making batts (by which term it is intended to include felts, strips, blankets and similar porous articles) to have a somewhat greater concentration of resin near the surface of the batt than at the center or vice versa as the fibers near the surface of the batt do not receive so much support from other fibers as do those at the center and it may be,

desirable to have the surface of the batt materially strengthened as the surface has to withstand handling, mechanical abrasion etc. to which the center of the batt is not subjected. In other instancesit may be desirable to have the interior of the batt rigidified while leaving the surface of the batt resilient. For the purpose of the following description the batts having difierent characteristics in different parts may be termed specialty batts.

The desiderata heretofore explained are accomplished by treating the glass wool batts (or the fibers as hereinafter disclosed) with a water solution of a phenolic aldehyde resinoid in the migratory condition. The treatment is relatively simple yet it involves phenomena which, to the best of my knowledge, have not heretofore been recognized or utilized.

Water solutions of phenolic aldehyde reaction products are knownbut heretofore have been used in such amounts and under such conditions to treat materials where the migratory condition of the products (provided the products were in such a condition that they would migrate) had no material influence on the finished article corresponding to the influence which the migratory characteristic has in producing batts of partially coated and partially uncoated glass wool. I have discovered that if a batt comprising fibers of glass W001, that is fibers of fused mineral substances which are non-porous and non-cellular and have a smooth surface, are treated with the said resinoid solutions, and then permitted to dry without substantially changing the condition of the resin, the liquefied resinoid will follow or migrate along the surface of the fiber and lodge at the point where the fiber contacts with another fiber. The

resinoid will remain at this point and harden thus forming a microscopic bead of binder at the intersecting points and there will be much less or substantially no binder on the fiber except at the points of intersection. This phenomenon cannot be taken advantage of wherever the surface of the fiber is rough. If the surface of the fiber shows depressions, the resinoid collects in the depressions and does not move to the points where the fibers cross; also where the surface of the fiber presents protuberances, as in the case of asbestos, th resinoid collects around these protuberances and does not migrate to the crossing points of the fibers. The word migratory and similar words are used herein to designate that condition of the resinoid or liquid-solvent mixture wherein the resinoid will be drawn along a smooth non-porous surface by the surface tension of the mixture as the mixture dries.

In treating the fibers in accordance with this invention it is possible to use a number of different resinoid and water compositions for instance those where water solubility is obtained through the use of various amounts of alkalies which form sufficient phenolates to keep the resin in solution, or by the use of phenol alcohols which are water soluble, but extraordinarily successful results are obtained by the use of a resin having an extremely small molecule or one which is capable of high dilution without the use of solution aids. In the case of the phenolates, the alkali may affect the fibers of the glass wool at the crossing points of the threads although a resinoid which is slightly on the alkaline side of the neutral point is preferred, for instance a resinoid having a pH value from 7 to 8.5 in a water solution containing 5% of resinoid, as the resinoid appears to migrate better in an alkaline solution than in an acidic solution. In the case of the phenol alcohols, after the solution has drawn to a bead at the fiber-contact points the phenol alcohols do not harden as quickly nor at as low temperatures as the straight resins. In the case of the phenol resins which are inherently water soluble, however, there are none of these disadvantages. The resin present in the water solution, particularly if it has a pH between 7 and 8.5, decreases the tendency of the water to wet the mineral fibers. In the changing system of dehydrating resin solution the migratory characteristic of the remaining liquid is constantly increasing as the dehydration increases until the point is reached where the resinoid precipitates. Furthermore, in the pure resinoid solution there are no salts or other non-binding materials which might have the tendency to cause the resin prematurely to deposit on the surface of the fibers either by a preferential precipitation of the resin or by a preferential precipitation of the other material which will drag down the resin or form a nucleus upon which the resin can precipitate. The pocket formed by crossing fibers thus attracts the most of the resinoid liquid and consequently a small amount of added binder will lock the fibers firmly into position.

The scientific explanation of the phenomenaliquid (theoretically twice as much liquid) than at the places where the fibers do not contact, as at the icontacting points each. fiber has contributed the amount of liquid in its film. Thus when the water begins to evaporate, the liquid film on any individual fiber will break at a point away from the point at which the fibers contact. In the usual batt there is such a myriad of fibers that the contact or intersection points are relatively close together although, particularly as seen under the microscope, they are appreciable distances apart, and the liquid film begins to thin down and finally breaks at a point substantially midway between the contact points. This breaking of the film forms two surfaces of the liquid film adjacent the breaking point and as the water continues to evaporate, these'surfaces retreat toward the nearest point of contact between the fibers. Several phenomena are utilized in the retreat of the liquid surfaces; one is that the presence of the resinoid in the water decreases the tendency of the water to wet the surface of the fibers, another is that the tendency of the solution to wet the surface of the fibers decreases with increasing resinoid concentration and another is that the surface tension of the solution increases with an increase of resinoid content. Thus the liquid carries the resinoid back toward the-contact points of the fibers until there is a small droplet of resinoid solution at the intersection points. The resinoid content of this droplet is quite concentrated as in a properly operated process for manufacturing the usual batts, it contains all of the resinoid which was in the liquid film originally distributed along the fiber from the point at which the film broke when the drying began. Finally the water evaporates from the droplet leaving a small bead of resinoid binding the fibers together 'at their intersection points. Under optimum conditions for the usual batts substantially all of the resin will be in the termine the concentration of the resinoid in the solution with'which the fibers or the batt is treated. As previously stated. the object is to have the resinoid in the usual batt only at the fiber intersection points and obviously where there are less fibers in 'a given volume of batt there are less intersection points and a greater distance between the intersection points. Thus the resin concentration should be low so that as the film on the surface of the fibers dries and the solution surface retreats to the fiber intersection points, the solution does not become'so concentrated that resin precipitates before the solution has contracted to the contact points, in other words the resin should be sufficiently soluble to remain in solution as the film dries from the fiber between the fiber-contact points. Where the batt contains more fibers in a given volume, there are obviously more fiber-contact points and the resinoid may be more concentrated in the solution as there is less distance for the solution film to retreat before collecting at a fiber-contact point.

of variables which have to be taken into consideration, for instance the solubility of the resinoid, the concentration of the resinoid in the solution and the amount of resinoid necessary to provide sufficient resinoid in the bead at the fiber-contacts to give the batt the required strength. the possible combinations of these variables but the rules governing the practice of the invention in order to obtain optimum results are relatively simple. From a practical standpoint there is obviously no use in having more than enough resinoid to form the beads which hold the fibers together. Ii, therefore, an inspection of the finished batt shows that there is resin on the fibers between the fiber intersection points, a more water soluble resinoid should be used and/or a more dilute solution in order that the resin does not precipitate out of the film before the film has retreated to the fiber-contact points. Precipitation oi' the resin may also be caused by the resinoid reacting under heat and becoming insoluble and therefore in order to Prevent the formation of intermediate deposits of resin, the batt should be dried more slowly and at a lower temperature.

It is also obvious that in the case of the usual batts the beads at the fiber-contact points need contain no more resinoid than is necessary to hold the fibers in place. The proper amount of resinoid in the finished batt may easily be determined by crushing a batt and observing under a microscope whether the fibers or the beads are broken. If the majority of breaks are in the fibers, the amount of resinoid may be decreased and if the majority of breaks are in the beads,

the amount of resinoid should be increased. Optimum results per unit of cost are obtained when the breaks are equally divided between fibers and beads as this indicates that the strength of beads and the strength of the fibers are approximately for any given type of batt; for instance a batt In practicing the invention there are a number 7 for heat insulation will-have sufficient fibers so that the air spaces between fibers are small enough to prevent the circulation of air to the extent necessary to giv optimum insulation. The size of the fibers should be such as to prevent the fibers breaking during handling of the batt or when other batts are placed upon it. From these points of view the principles upon which batts are constructed are understood. The dimcuity, heretofore, has been that the batts would not maintain their shape, for instance a lower batt placed within the wall of a building'would gradually compress under the weight of the upper batts and the entire insulation would settle.

When made according to the present invention, however, the batts have maximum strength and resistance to deformation at the least cost and while there may be som deformation due to weights placed upon the batts and the yield of the fibers in the batts, the amount of deformation is limited.

, The resinoid may be applied to the mineral wool fibers in a number of different ways. The resinoid solution may be sprayed onto the fibers while the fibers are hot; that is as soon as the fibers issue from the furnace nozzle. In this case It is difficult to give examples of all,

it is desirable to use an extremely dilute solution as the water quickly cools the fibers and prevents the reslnoid from setting or losing its migratory characteristic.v In case the fibers are made by drawing from-the nozzle, they may be led through a tank containing the reslnoid solution. Also the fibers may be blown into a container into which the reslnoid solution may simultaneously be sprayed, thus coating the fibers. The fibers may also be formed into batts (either finished to size or semi-finished) which are then either dipped into the reslnoid solution and drained or sprayed with the solution. The spray may be of such force as to Dass'entirely through the batt from one side to the other and the passage may be assisted by a vacuum applied on the side of the batt away from the spray gun. Any other method of coating the fibers may be used.

Before the reslnoid has lost its migratory characteristic the batt is compressed to the desired size provided a denser batt is required than would be obtained merely from the natural laying of the fibers. The compression can be effected without breaking the fibers as the fibers may be quite resilient and the binder has not yet hardened. After the batt has been given the required dimensions, the water is evaporated during which the film n the fibers retreats to the fiber-contact points. Continued heating sets the reslnoid and once the beads of reslnoid are formed at the fiber-contact points the entire process may be accelerated by the application of a stronger heat. It is also possible, for instance by working quickly and using a reslnoid which is only slowly reactive or one which is highly water-soluble, for instance a phenol alcohol or a straight resin which has such a small molecule size that it does not quickly become insoluble, to utilize the residual heat of the fibers as they issue from the furnace nozzle, to evaporate the water irom'the film. The batt should preferably be formed to the desired dimensions, however, while the resinoid is in the migratory condition and sufiicient water is pres ant to let the reslnoid migrate. After the reslnoid sets the batt will substantially retain its given dimensions allowing, of course, for the springback which will occur when the compression is released from a batt which was compressed during setting of the resin. 1 However, this springback may be very small as the fibers have been bound in the positions given them during compression of the batt and such spring-back as: occurs is that permitted by the short lengths of fibers between the beads of binder. Furthermore the spring-back occurs mostly at the surface of the batt where a fiber is not bound by so many contact bonds as an interior fiber.

Specialty batts may also be made quite simply using these reslnoid water solutions, that is batts which are comparatively rigid in one portion and have the spring-back flexibility and resiliency in another portion. It may be desirable for thebatt to have a rather rigid interior portion so that it will hold its general shape yet be somewhat resilient at the exterior portion so that it.will yield, for instance a batt which is used to insulate the wall of a shingled building may be required to have a quite rigid center plane so that the batt will support the weight of the batts above it yet the exterior portion of the batt should be relatively flexible and resilient so that the surface lies snugly against the rough and irregular ends of the shingles presented within the wall. In some instances it may also be desirable to have one side of the batt relatively rigid and the other side of "the batt yieldable and fiexible, or to have the exterior of the batt rather rigid'and the interior yieldable and flexible. But, although the batt should be flexible and yieldable in certain portions, these portions should not take a permanent deep set as they would if the fibers were not bonded at the fiber intersection points.

Batts which are relatively resilient at one portion and relatively rigid at another portion may easily be obtained from the same reslnoid solution by operating the process of treating the batts with a solution of a reslnoid in the migratory condition to take advantage of the migratory character of the resin in one portion of the batt and its tendency to' precipitate in another portion of the batt.

It will be understood that the glass wool fibers may be made of such small diameter and of such materials that they are relatively yieldable, flexible and springy, If two identical smooth surfaced glass wool fibers are coated to the same thickness with the same reslnoid water solution and the coating on the first fiber is dehydrated without affecting the migratory character of the resin, for instance if the coating is dehydrated slowly so that the coating can retreat and the resin is so soluble that it does not precipitate as the coating shrinks, the coating film will draw up into a head which will deposit a bead of reslnoid on the fiber when the water finally evaporates. This will leave the majority of thefiber in its original flexible and springy condition. However, if the film on the second fiber is dehydrated quickly, or if the reslnoid is chemically advanced P toward its final water insoluble state, for instance by heat, without causing shrinkage of the film, the reslnoid will precipitate as a film on the fiber and rigidify it; In this case there will be substantiallyno migration and strength at the fiber-contact points will be obtained only to the extent that the united films ailord such strength. However, excess resin may be used to give such strength as may be desirable at the fiber-com tact points.

Taking advantage of these characteristics, I am enabled to use the same water reslnoid solution and yet obtain batts having rigidity in one portion and flexibility in another portion. To obtain a batt which has a relatively stifi center portion and a more resilient outer portion, dry warm air may be blown gently from opposing surfaces of the batt toward the center from opposing air nozzles. The dryness of the air dehydrates the films on the fibers near the surface of the batt and causes the films to retreat to the fiber contact points and finally hardens the reslnoid into beads at the fiber-contact points. The moisture picked up by the air at the surface of the batt prevents substantial dehydration of the films at thecenter of the batt but the heat at the center of the batt causes the resin to react and precipitate on the fibers as a film which rigidifies the fibers. Because of the spreading action of the opposing jets of warm air, the interior portion of the batt is subjected to a greater heat-temperaure efl'ect than is the surface of the batt and thus migration and beading oi the reslnoid may be effected on the surface of the batt and filming or tubing effected at the center of the batt. It

which is individual for each fiber and separate from other tubes except where the fibers and their tubes intersect.

If it be desired to rigidity the interior portion of the batt to astiii greater extent the batt may be passed between opposing spray heads and the spray of resinoid solution may be driven into the batts under considerable pressure. The force of the spray will prevent the deposition of any large amount of the solution withinthe outer portions of the batt but in the center plane of the batt, where the opposing sprays meet, the larger amount of the solution will deposit. Sufiicient resinoid may thus be deposited at the cen ter portion of the batt to provide excess resinoid whereby the interior fibers may both be bound at the fiber-contact points and coated to form the tubes and thus the center portion will be strengthened, leaving the outer portions more resilient.

It is also possible to strengthen the interior portions of the batt and leave the outer portions more resilient by driving the spray of a relatively concentrated solution of a highly soluble resin to the interior of the batt and then spraying, the batt with pure water which does not penetrate to the interior of the batt. This gives a more concentrated resin solution at the interior portion of the batt than at the outer portion Then the dehydration may be effected to concentrate the resinoid in the interior films to such a point that it precipitates as a film or tube on the fibers but the films at the exterior portions of the batt will dehydrate relatively so much more slowly that the resinoid will have an opportunity to migrate and thus bead at the fiber-contact points instead of filming along the length of the fibers.

If it is desired to rigidify the outer portions of a batt while retaining a resiliency at the inner portions. such result may be effected by fiowing warm humid air against the surfaces of the batt at an angle. Greater or less penetration of the batt may be effected depending upon whether the air impinges upon the surface more nearly perpendicular or more nearly parallel to the surface, respectively. The heat causes the resinoid to precipitate as a resinoil film on the fibers and the moisture prevents the dehydration and retraction of the solution film to form beads. The interior of the batt may be permitted to dry slowly thus affording the resinoid solution an opportunity to retreat and form heads at the fiber-contact points. It is also possible to strengthen the exterior of the batt with excess resinoid by spraying the batt with a gentle spray of the resinoid solution or by spraying at an angle to the surface of the batt so that more of the resinoid solution is retained at or near the surface. Steam may be used instead of warm air to treat the batts, wet steam being used to obtain heat without dehydration and superheated steam being used to effect a measure of dehydration.

Thus by using the water-resinoid solutions with the fibers disclosed I am enabled to produce a batt strengthened with resinoid and place the resinoid where it is desired and determine the type of coating or bond which is to be formed and the type of batt which is to be produced; and it is possible to accomplish these results with the use of a single, low cost material by a very simple treatment.

The resinoid solution used in accordance with I this invention may contain from 2% to by weight of resinoid which may be a phenol alcohol, a phenolate or a water soluble resin, formstance of thetype disclosed in the Bender Patent No. 2,034,457 dated March 1'7, 1936 or in my copending application Serial Number 68,915 filed March 14, 1936, now Patent No. 2,190,6'72, dated February 20, 1940.

A suitable phenol alcohol may be made by mixing one mo]. of phenol, two mols. of formaldehyde and one-half moi. of barium hydroxide. The formaldehyde may be in the usual 37% water solution and the weight of barium hydroxide should be calculated taking into account that the commercial material contains eight mols. of combined water per moi. of barium hydroxide. The mixture is permitted to stand at room temperature for two or three days or until analysis shows that from 90% to 95% of the formaldehyde has reacted. The barium hydroxide may be neutralized with a dilute acid, for instance sulphuric if it be desired to precipitate barium sulphate and remove the salt.

A suitable phenylatemay be made by mixing one moi. of phenol, 0.9 mol. of formaldehyde and 0.3% of oxalic acid based on the phenol, This mixture is refluxed at atmospheric pressure for five or six hours until substantially all of the formaldehyde has reacted. A 10% sodium hydroxide. solution in water is then added in sufficient quantity to give 0.5 to 0.6 mol. of sodium hydroxide which produces the desired water solubility., About 0.6 mol. of sodium hydroxide is necessary in order to hold the resinoid in solution to as low a percent as 2% resinoid in 98% water. In order to make this resin reactive it is also necessary to add into the water about 0.2 mol. of formaldehyde.

With regard to the type of resin disclosed in the Bender Patent No. 2,034,457, this resin may become cloudy when diluted to a point where it contains less than 30 parts of resin per 70parts of water. To overcome this cloudy eifect about 5% of alcohol (methyl or ethyl alcohol preferred) or acetone on the total solution may be added. Instead of the alcohol or acetone about 6% of caustic based on the resin may be added. However, it is possible to use the resin of the Bender patent in the cloudy state as after the solution is applied to the fibers, the dehydration of the coating films concentrates the solution to the point where there is more than 30% resin to 70% of water, in which case the cloud disappears even though no caustic or alcohol or acetone be added.

For the usual batts a solution containing approximately 4% of resinoid in 96% of water is satisfactory. Higher or lower resin concentrations may be used in accordance with the principles hereinbefore stated. Viscosities of the resinoid-solvent solutions should be less than about 10 centipoises and may range from about 1.1 centipoises, to 10 centipoises as applied to the batt. Also the water may be somewhat diluted with alcohol or other water miscible resinoid solvents although water alone is greatly preferred on account of its low cost and its high surface tension. The usual batt having the resinoid concentrated at the fiber-contact points made according to my patent application Serial Number 68,915 (7.5 parts of resin and parts of water) were dissolved in 300 parts of water and applied to a batt of glass wool by immersing the wool in the solution and draining. All of the fibers in the batt were thus coated with the water-resin solution. The treated batt was baked in an oven at 65 C. for two hours during which the resin formed heads at the fiber crossings and dried to a sticky condition. A further bake of six hours at 210 C. hardened the beads. Example II.-Glass wool was treated as in Example I except that the treated batt was dried at 080 C. for fifteen hours and then baked at 260 C. at which temperature the resin set D in from 15 to 20 seconds.

It is to be understood, however, that the invention is not to be limited to the above examples but is to be construed as broadly as the following claims taken in conjunction with the prior art may allow.

What is claimed is:

1. Process of making a batt containing intersecting smooth surfaced non-cellular fibers of glass wool which comprises coat ng the fibers with a dilute watery alkaline solution of a phenol cause the coating to migrate to the intersection points of the fibers and subjecting the coating on another, portion of the fibers to a more humid heat to cause the coating to deposit the resinaldehyde resinoid, said solution having a viscosity between approximately 1.1 centipoises and approximately 10 centipoises, dehydrating the coating on one portion of the fibers sufficiently slowly to cause the coating to migrate to the intersection points of the fibers and dehydrating the coating on another portion suificiently quickly to cause the resinoid to deposit from the solution in situ.

2. Process of making a batt containing intersecting smooth surfaced non-cellular fibers of glass wool which comprises coating the fibers with a dilute watery alkaline solution of a phenol aldehyde resinoid, said solution having a viscosity between approximately 1.1 centipoises and approximately 10 centipoises, subjecting the coating on one portion 01 the fibers to a dry heat to old from the solution in situ.

3. Process of making a batt containing intersecting smooth surfaced non-cellular fibers of glasswool which comprises coating the fibers in one portion of the batt with a dilute watery alkaline solution of a phenol aldehyde resinoid, said solution having a viscosity between approximately 1.1 centipoises and approximately 10 centipoises, coating the fibers in another portion of the batt with a heavier coating of a watery solution of a phenol aldehyde resinoid, dehydrating the coating in the first named portion of the butt sufficiently slowly to cause the coating to migrate to the intersection points of the fibers and de hydrating the coating in the second named portion of the batt sufliciently quickly to cause the resinoid to deposit from the solution in situ.

4 Process of making a batt containing intersecting smooth surfaced non-cellular fibers of glass wool which comprises coating the fibers in one portion of the batt with a dilute watery alkaline solution of a phenol aldehyde resinoid, said solution having a viscosity between approximately 1.1 centipoises and approximately 10 centipoises, coating the fibers in another portion .of the batt with a heavier coating of a watery solution of a phenol aldehyde resinoid, dehydrating the coating in the first named portion of the batt sufiiciently slowly'to cause the coating to migrate to the intersection points of the fibers and subiecting the coating in the second named portion of the batt to humid heat to prevent substantial dehydration of the coating in the second named portion of the batt until the resinoid has deposited in situ from the solution.

VIRGIL E. MEHARG. 

